That's a lot of questions in one post so let me answer some of them without trying to confuse you (<-- not an insult).
Meedio and MeediOS are two separate programs
Meedio is no longer in development. But plugins and themes are still in development for Meedio. The latest version you of Meedio is 1.41 which you can download. I assume that's the version you have. When you say Meedios, I assume you mean Meedio.
MeediOS is an open source program that models Meedio. It's actively being worked on however it's been slow. MeediOS is not functional at this point and is not ready for us to use (especially in a carPC).
After installing Meedio, it automatically sets itself up to install plugins. So once Meedio is installed, you can download a plugin, open it like any other file, and Meedio will install it. If everything goes well, you'll get a message saying it was successful. Afterwards, run configure.exe (located in your Meedio folder) and you'll see the plugin in one of the tabs. In fact, you'll see all the plugins on the plugin tab. It's this tab which allows you to activate,deactivate and configure plugins.
Knowledge of programming code is not required to use plugins. But if you want to write your own plugin then yes, knowledge of code is required.
I do not know why Meedio is crashing for you. But the best place to ask all these questions is the forums. The best place to read is the wiki and the forums too. The forums are very active and people are very willing to help you out. I suggest you go over there to see if someone has a similar problem.
Meedio Main Site
PS I'm not brushing you off to another forum, please come back here and ask questions if you need more help. I currently run Meedio as my carPC front end.